Processed semiconductor wafers typically comprise an array of substantially isolated integrated circuitry which are individually referred to as "die" or "chips." Some circuits are formed on boards, such as printed circuit boards, such as where the cost of designing and manufacturing an integrated circuit chip is too high relative to the size benefit. These chips or boards define various circuits for use in computers (e.g., video cards, sound cards, modem cards, etc.), televisions, telephone systems, and many other electronic devices. The chips or cards also define the finished circuitry components of, for example, processors and memory circuits. Common types of memory circuits are DRAM and SRAM chips.
After a semiconductor wafer has been fabricated, not all chips provided on the wafer prove operable, typically resulting in less than 100% yield. Accordingly, individual dies must be tested for functionality. The typical test procedure for DRAM or SRAM circuitry is to first access the device via bonding pads on the individual die. Thereafter, the wafer is subjected to test probing whereby the individual die are tested for satisfactory operation. Inoperable die are typically marked by an ink mark. After testing, the wafer is cut into individual die. The operable, non-marked die are collected.
The operable individual die are then assembled in final packages of either ceramic or plastic to define a packaged integrated circuit or device. After packaging, the integrated circuits are loaded into burn-in boards which comprise printed circuit boards having individual sockets. The burn-in boards are placed into a burn-in oven, and the parts are subjected to burn-in testing during which the die are operated for a period of time at different temperature cycles, including higher than operating temperatures. The die are stressed to accelerate their lives in an effort to identify the weak die which are likely to degrade and fail under these tests. Manufacturers predict early failures, known as "infant mortalities", to occur within a predetermined period of time of the burn-in cycle. Burn-in testing is typically conducted for a period of time sufficient to reveal these infant mortalities. For example, if infant mortalities are expected to occur within twenty-four or forty-eight hours of burn-in testing, the burn-in tests can be completed within such time periods. In this manner, semiconductor wafer manufacturers can effectively test the quality of their integrated circuits in a reasonable time frame prior to shipping the integrated circuits to consumers.
More particularly, the failure rate for a semiconductor device as a function of time generally follows what is known as a "bathtub-type curve". The initial or infant mortality failure rate for die is very high at the start, and flattens out to near zero during a mid-time period, such as from one month through a period of 10 to 12 years, and then goes back up. In other words, if the integrated circuit survives the first one to five months or so of operation, it is highly probable that it will provide flawless operation through the tenth or twelfth year. Thereafter, usually after the expected lifetime of the device, material or other changes in the die cause the failure rate to increase exponentially, thus providing the bathtub shaped curve.
Burn-in testing can be conducted in either what is known as the static method or by a dynamic method. In both, the packaged die is electrically stressed under elevated temperature (e.g., 125.degree. C.) for a given period of time (e.g., 24 hours) sufficient to test the die. Under a static electrical test, the die is subjected to an operating voltage that is much higher than the normal operating voltage. For example, the V.sub.cc node of the die may be subjected to an operating voltage of seven volts instead of the normal V.sub.cc voltage of three to five volts, while the V.sub.ss node of the die is held at ground. Operability is determined at the end of the test.
Under dynamic testing, individual devices are exercised on and off throughout the burn-in period, and the die is constantly monitored. Operability is determined during the test.
On a burn-in board, several receptacles are provided on a burn-in board (e.g., two feet by three feet in size), and the individual packages are received. Wiring extends from these individual receptacles/devices to one edge of the board where they connect outwardly to the testing and intelligence cycling circuitry. These long lengths of line create undesired parasitics such as unwanted noise, capacitance, resistance, inductance and crosstalk.
As described above, the die are subjected to a preliminary wafer-level test before sawing into individual die, and a burn-in test after separating and packaging of the individual die. Each of these two separate tests require some physical connection with a testing apparatus. During the wafer-level test probes are employed to directly contact bonding pads. During the burn-in testing, each individual chip is inserted into a socket on a burn-in board for the test.
Attention is directed to commonly assigned U.S. patent application Ser. No. 07/979,607, filed Nov. 20, 1992, titled "Testing and Burn-In of IC chips Using Radio Frequency Transmission," which is incorporated herein by reference.